Control apparatus



Oct. 25, 1966 P. GUIFFRIDA CONTROL APPARATUS 2 Sheets-Sheet 1 Filed NOV. 5, 1963 United States Patent 3,281,812 CONTROL APPARATUS Philip Guiffrida, North Andover, Mass, assignor to Electronics Corporation of America, Cambridge, Mass., a corporation of Massachusetts Filed Nov. 5, 1963, Ser. No. 321,576 Claims. (Cl. 340-214) The present invention relates to improved control apparatus and more particularly to condition responsive systems such as those useful in supervising fuel burning systems, and to means for insuring reliable operation of the sensory and signal modifying portions of such systems.

In condition responsive systems of the type employed for the supervision of flame established in a combustion chamber, it is desirable that the supervising system react very quickly to the presence or absence of flame so that the fuel valve may be closed quickly and prevent an excessive amount of unburned fuel from accumulating in the combustion chamber in the absence of flame. Flame sensing systems which have the desirable rapid response to the presence or absence of flame are well known, but such systems are susceptible to component malfunction and may cause the flame detecting system to falsely indicate the presence of flame. Should such a malfunction occur in a system supervising flame in a combustion chamber, an unsafe condition might arise as the system, in the event of flame failure, would continue to react as if flame was present and permit the continued introduction of raw fuel into the furnace chamber. The accumulated raw fuel could be ignited explosively, either by the hot refractory or upon an attempt to reignite the burner for ex ample, with disastrous results.

Industry standards specify that approved combustion control systems must operate with a maximum time delay of four seconds between flame failure and shut down of the fuel flow to the supervised combustion chamber. Component checking arrangements which check the operability of the system by simulating flame failure therefore must complete their cycle through flame relay drop out and flame relay pickup within that time. While checking arrangements have been devised for flame sensors operating at power frequency such as flame rods or photocells, no commercially successful checking arrangement, to my knowledge, has heretofore been devised for circuitry of lower frequency response such as the flame flicker type of combustion supervision circuitry employing a lead sulphide type of infrared radiation sensor, which operates with a signal in the order of five to twenty-five cycles per second.

Accordingly, it is an object of this invention to provide an improved condition sensing system incorporating component checking arrangements whereby the operation of the condition sensing system is regularly checked to insure that the system is not falsely indicating the presence of the condition to be sensed.

Another object of the invention is to provide a novel and improved flame detecting system particularly useful with flame sensors responsive to infrared radiation.

Other objects, features and advantages of the invention will be seen as the following description of a preferred embodiment thereof progresses, in conjunction with the drawings, in which:

FIG. 1 is a schematic diagram of the condition responsive system constructed in accordance with the invention for use in a combustion supervision arrangement;

FIG. 2 is a timing diagram indicating the states of various components in the control system of FIG. 1 in a sequence of operation; and

FIG. 3 is a schematic diagram of circuitry of a second combustion control system constructed in accordance with the invention.

With reference to FIG. 1, the reference numeral 10 designates flame from a fuel burner in a combustion chamber that is under supervision. Disposed in optically coupled relation to the flame is a flame sensor 12 in the form of a lead sulphide cell and positioned between the flame 10 and the sensor 12 is a shutter 14 which is continuously driven in rotation at a one revolution per second rate by motor 16. The shutter has an arc of approximately 180 which is opaque to radiation to which sensor 12 is responsive, and when interposed between the flame and the sensor simulates a flame failure condition. Other cyclically operative devices may also be employed to simulate flame failure conditions at regular intervals.

The lead sulphide sensor 12 is connected by means of lines 18 and 20 to a frequency selective circuit of the type disclosed in the US. Patent 2,811,711. Line 13 is also connected through a load resistor 22 to a source of DC. high voltage obtained through diode 24 and a series of smoothing capacitors from a tap of the secondary winding 26 of transformer 28. The transformer primary winding (not shown) is connected by conventional means to a 120 volt A.C. source.

The frequency selective circuit is a high input impedance electronic amplifier which includes a pair of amplifier stages 30, 32. The input coupling capacitor 34 and interstage coupling capacitors 36, 38 cooperate with capacitive feedback circuits 40, 42, 44, 46 to provide a band pass amplifier circuit which peaks at 10 c.p.s. and has significant response only to signals in the five to twenty-five cycle per second frequency range.

The output from coupling capacitor 38 is applied through an integrator circuit which includes diode 50 and capacitor 52 and resistor 54 to a bistable vacuum tube circuit. A negative bias is applied to the junction 56 of the integrator circuit through diode 58 from the twelve volt tap 60 of the transformer secondary 26. (Filament voltage is also obtained from this tap.) This arrangement maintains triode stage 62 of the bistable circuit in cut off condition in the absence of suflicient charge on capacitor 52 to overcome the negative bias supplied by diode 58 to junction 56.

A second triode stage 64 has its cathode 66 connected through resistor 68 to the anode 70 of triode stage 62. Grid 72 of triode stage 64 is directly connected to anode 70 and a capacitor 74 is connected between the cathode 66 and grid 72.

The anode 76 of stage 64 is connected through a load resistor 78 to a second D.C. source of high voltage obtained from secondary Winding 26 through diode 80 and capacitor 82.

Connected to the lower terminal of the load resistance 78 is one terminal of an electric charge storage capacitor 84. The other terminal of capacitor 84 is connected to an electric charge storage control switch in the form of diode 86 and an electric charge transfer control switch in the form of diode 88. Connected across these diodes is a capacitor 90 in parallel with a load control relay 92 which is maintained in picked up condition as long as the charge on capacitor 9% exceeds a predetermined level. A choke 94 is connected between diode 86 and the upper terminal of resistor 78. (Choke 94 presents a high impedance to A.C. currents resulting from failure of power supply filter condensor 82, for example, which in the absence of choke 94 might cause the flame relay to pick up, and thus provides a margin of reliability for the circuitry.)

In operation, with the system in standby condition so that the negative bias via diode 58 maintains stage 62 in non-conducting condition and stage 64 in conducting conw dition, a voltage drop is produced across resistor '78 and the resulting current flow through diode 86 charges capacitor 84. When sensor 12 sees infrared radiation from flame 10, its resistance changes so that a pulsating change of voltage is applied over lines 18 and 28 to the band pass amplifier. The infrared radiation of combustion flame has been found to vary at a flicker frequency between five and twenty-five cycles per second and, as the amplifier is tuned at ten cycles per second, the amplifier passes a signal representative of radiation through capacitor 38. The positive half cycles of this radiation signal are passed by diode 58 for storage by capacitor 52. Capacitors 38 and 52 are related in size (typical values being capacitor 38 0.022 microfarad and capacitor 52 1.0 microfarad) so that two or more flame flicker pulses typically are required to charge capacitor 52 to a potential suflicient to overcome the negative bias and supply a signal through grid isolation resistor 54 to cause stage 62 to conduct. This sequence of flame flicker pulses relative to the conduction of stage 62 is indicated in FIG. 2.

When triode stage 62 does conduct the resulting current flow charges capacitor '74 such that the grid 72 of triode stage 64 becomes negative with respect to cathode 66 and stage 64 ceases conduction after a further time delay as indicated in FIG. 2. While stage 64 was conducting the voltage drop across resistor '78 caused capacitor 84 to become fully charged with the indicated polarity through the circuit including diode 86 and inductance 94. When stage 64 ceases conduction the voltage drop across load resistor 78 which has maintained the charge potential on capacitor 84 terminates, and the resulting potential transition causes diode 86 to become reverse biased. Diode 88 forward biases so that a portion of the charge on capacitor 84 is transferred to capacitor 90 as a function of their relative capacities. Suitable values for these capacitors are forty microfarads each. The charge imparted to capacitor 98 produces sufficient potential to cause solenoid 92 of the flame relay to be energized and pick up relay contacts 96 which close and energize the indicator or other suitable load 98. Capacitor 98 starts to discharge both through the solenoid 92 and choke 94, but the circuit parameters are such that the flame relay will remain in picked up condition for approximately 3 sec.

To restore capacitor 84 to charged condition it is necessary for stage 64 to again conduct, which occurs when stage 62 becomes non-conductive. This occurs whenever the frequency selective circuits pulse output ceases, due either to actual flame failure or to simulated flame failure caused by shutter 14. As shown in FIG. 2, this occurs every second and has a duration of approximately one-half second. As soon as the c.p.s. input signal to the frequency selective circuit is interrupted its output ceases and the negative biasing potential overcomes the residual charge on capacitor 52 so that stage 62 ceases conduction and stage 64 conducts. The exponential discharge of capacitor 84 is converted to an exponential charge but diode switch 88 closes so that the charge on capacitor 98 is substantially unaffected. The circuitry is quickly restored to initial state and then the shutter ends the simulated flame failure condition. The circuit is delayed response to flame flicker signals again transfers charge from capacitor 84 to replenish the charge on capacitor 90 so that the flame relay holds in contacts 96, maintaining the load 98 in energized condition.

Should flame failure occur, capacitor 52 would quickly be discharged so that stage 62 is held in non-conduction and stage 64 in conduction. As the charge on capacitor 90 is not regularly replenished its potential drops below the hold in potential of the flame relay and contacts 96 open, de-energizing the load. However, on component failure which causes the frequency selective circuit to continue charging capacitor 52, for example, stage 64 is held in non-conducting condition so that capacitors 84- and 90 both discharge and again the flame relay drops out, well within three seconds from the time of component failure.

The frequency and duration of the simulated flame failures employed are related both to the input frequency from the flame and the permitted system response delay the simulator frequency (one c.p.s.) being less than the lowest flame frequency to which the system responds (five c.p.s.) but more than the system response delay (one-third c.p.s. in frequency terms) while the duration of simulated flame failure is effectively more than half of each simulator cycle (in excess of one-half second). This system and timing relation provide for the first time a component checking arrangement for rapidly responsive burner supervision systems employing the flame flicker principle. While the system has particular advantages in such systems, its use is not limited thereto. For example, it may also be employed in systems of the type shown in FIG. 3 in which a detector 112 of the avalanche discharge type is disposed to sense radiation from flame 118 in a combustion chamber. A shutter 114 of the same type as shut-- ter 14 shown in FIG. 1 is disposed between the flame 118 and the detector 112 and driven continuously by motor 116 so that it is interposed regularly between the flame and the detector 112.

The detector is connected in series with the secondary Winding 118 of an autotransformcr. (A small current limiting resistor may be employed in series with the detector.) The autotransformer is energized from a conventional power source applied at terminals 122 and connected in series with this power source are a pair of readout impedances 124, 126 and a resistor 128. A capacitor 130 is connected in parallel with the source. When the detector breaks down in avalanche discharge in response to radiation produced by flame 110, the pulse of current flow in the secondary circuit is inductively coupled into the transformer primary circuit. The readout impedances 124, 126 present a higher impedance to this pulse than to the sixty cycle transformer energizing signal and hence the signal is coupled through one of diodes 132 (depending on the polarity of the pulse) to the output line 134-.

Coupled to this output line is a frequency selective circuit which includes a silicon controlled switch 136 whose control electrode 138 is connected to an input circuit ineluding capacitor 140 and resistors 142 and 144. This control electrode 138 has a DC. bias applied from the energizing source through diode 146 and resistor 148 which maintains the control electrode at a potential slightly negative with respect to the cathode of the switch 136. The switch, when the control electrode 138 has a relatively rapid rise time pulse applied thereto, conducts and applies a voltage transition to the base of control transistor 158 to turn that transistor off.

l/Vhile the transistor is conducting, a voltage drop is produced through load resistor 178 so that capacitor 184 is charged through diode 186 and inductance 1%. The transistor 158 is normally in conduction by the positive biasing of the base 152 of transistor 158 with respect to its emitter. This conduction produces a voltage drop in the load resistor 178 which enables the capacitor 184 to be charged through diode 186 and inductance 194. When the transistor is driven into non-conducting condition as a result of turn on of switch 136, the voltage drop across resistor 178 is removed causing the potential on the left hand lead of capacitor 184 to rise with a similar rise in potential on the right terminal of the capacitor so that diode 186 becomes back biased and diode 188 becomes forward biased. With the forward biasing of diode 188, a portion of the charge on capacitor 184 is transferred to capacitor 198 which is sufficient to energize the solenoid 192 of the flame relay and close contacts 196 to energize the load device 198 (an indicator or a fuel valve solenoid, for example).

When the shutter 114 is interposed between the flame 118 and the detector 112, the output pulses, holding the control electrode 138 of the switch 136 in enabled condition, will cease allowing the switch to open. Transistor 150 then conducts for a period in excess of the duration of the simulated flame failure produced by the interposition of shutter 114 between the flame 110 and detector 112 and replenishes the charge on capacitor 184 while the capacitor 190 is isolated from that charging circuit. When the detector 112 again sees flame 110, the silicon controlled switch 136 will be again actuated to conduct and turn off the transistor 150, producing a transfer of charge from capacitor 184 to capacitor 190 and replenishing that charge so that the flame relay contacts remain closed.

As in the case of the embodiment of FIG. 1, should the circuitry, by reason of flame failure or component failure, not regularly switch transistor 150 between a conducting state and a non-conducting state, suflicient to maintain the necessary charge storage relationship of capacitor 190 relative to solenoid 192, the flame relay will drop out and open contacts 196 to de-ergize the load device 198.

While a preferred embodiment of the invention and modifications thereof have been shown and described, further modifications thereof will be obvious to those skilled in the art. Therefore it is not intended that the invention be limited to the disclosed embodiments or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. Burner control apparatus for use with a fuel burner comprising flame sensing means for producing an output signal having a predetermined frequency component in response to sensed flame,

said flame sensing means adapted to be disposed to sense flame produced by said fuel burner in a combustion chamber,

frequency selective means for producing a control signal only when signals applied thereto include said predetermined frequency component,

coupling means for applying output signals produced by said flame sensing means to said frequency selective means, first demodulator means coupled to the output of said frequency selective means for modifying said control signal to provide a steady state output signal when signals applied to said frequency selective means from said flame sensing means include said predetermined frequency component,

means arranged to cyclically simulate the absence of flame in said combustion chamber at a rate substantially less than the said predetermined frequency component to periodically interrupt said demodulator output signal,

and second demodulator means responsive to said output signal from said first demodulator means to pro vide a steady state control device operating signal when said first demodulator output signal is interrupted at regular intervals comprising,

first electric charge storage means coupled to said first demodulator means and responsive to said first demodulator output signal to store electric charge as a function of the absence of said first demodulator output signal,

second electric charge storage means,

a control device coupled to said second storage means adapted to assume a first state indicative of the presence of flame in said combustion chamber when the electric charge stored in said second storage means is above a predetermined level,

and a second state indicative of the absence of flame in said combustion chamber when the electric charge stored in said second storage means falls below said predetermined level,

and means to transfer electric charge from said first storage means to said second storage means only in response to the presence of said first demodulator output signal to cause said control device to assume said first state.

2. The burner control apparatus as claimed in claim 1 wherein said simulator means includes a rotatable shutter having a first sector opaque to the flame component being sensed and a second sector transparent to the flame component being sensed,

end means for continuously rotating said shutter.

3. The control apparatus as claimed in claim 2 wherein the areas of said first and second sectors are substantially equal.

4. The apparatus as claimed in claim 1 wherein said first demodulator means includes a resistance capacitance network coupled to the output of said frequency selective means.

5. The apparatus as claimed in claim 4 wherein said frequency selective means has significant response only to signals in the 525 cycle per second range as applied thereto from said flame sensing means, and the operating rate of said simulator means is in the order of 1 cycle per second.

References Cited by the Examiner UNITED STATES PATENTS 2,798,213 7/1957 Rowell 340--228 X 2,798,214 8/1957 Rowell 340-214 X 2,807,008 9/1957 Rowell 340-228 X 2,994,859 8/1961 Klein 340-228 3,143,161 8/1964 Graves et al 340-214 X NEIL C. READ, Primary Examiner.

D. YUSKO, Assistant Examiner. 

1. BURNER CONTROL APPARATUS FOR USE WITH A FUEL BURNER COMPRISING FLAME SENSING MEANS FOR PRODUCING AN OUTPUT SIGNAL HAVING A PREDETERMINED FREQUENCY COMPONENT IN RESPONSE TO SENSED FLAME, SAID FLAME SENSING MEANS ADAPTED TO BE DISPOSED TO SENSE FLAME PRODUCED BY SAID FUEL BURNER IN A COMBUSTION CHAMBER, FREQUENCY SELECTIVE MEANS FOR PRODUCING A CONTROL SIGNAL ONLY WHEN SIGNALS APPLIED THERETO INCLUDE SAID PREDETERMINED FREQUENCY COMPONENT, COUPLING MEANS FOR APPLYING OUTPUT SIGNALS PRODUCED BY SAID FLAME SENSING MEANS TO SAID FREQUENCY SELECTIVE MEANS, FIRST DEMODULATOR MEANS COUPLED TO THE OUTPUT OF SAID FREQUENCY SELECTIVE MEANS FOR MODIFYING SAID CONTROL SIGNAL TO PROVIDE A STEADY STATE OUTPUT SIGNAL WHEN SIGNALS APPLIED TO SAID FREQUENCY SELECTIVE MEANS FROM SAID FLAME SENSING MEANS INCLUDE SAID PREDETERMINED FREQUENCY COMPONENT, MEANS ARRANGED TO CYCLICALLY SIMULATE THE ABSENCE OF FLAME IN SAID COMBUSTION CHAMBER AT A RATE SUBSTANTIALLY LESS THAN THE SAID PREDETERMINED FREQUENCY COMPONENT TO PERIODICALLY INTERRUPT SAID DEMODULATOR OUTPUT SIGNAL, AND SECOND DEMODULATOR MEANS RESPONSIVE TO SAID OUTPUT SIGNAL FROM SAID FIRST DEMODULATOR MEANS TO PROVIDE A STEADY STATE CONTROL DEVICE OPERATING SIGNAL WHEN SAID FIRST DEMODULATOR OUTPUT SIGNAL IS INTERRUPTED AT REGULAR INTERVALS COMPRISING, FIRST ELECTRIC CHARGE STORAGE MEANS COUPLED TO SAID FIRST DEMODULATOR OUTPUT SIGNAL TO STORE ELECTRIC CHARGE AS A FUNCTION OF THE ABSENCE OF SAID FIRST DEMODULATOR A FUNCTION OF THE ABSENCE OF SAID FIRST DEMODULATOR OUTPUT SIGNAL, SECOND ELECTRIC CHARGE STORAGE MEANS, A CONTROL DEVICE COUPLED TO SAID SECOND STORAGE MEANS ADAPTED TO ASSUME A FIRST STATE INDICATIVE OF THE PRESENCE OF FLAME IN SAID COMBUSTION CHAMBER WHEN THE ELECTRIC CHARGE STORED IN SAID COMBUSTION CHAMBER WHEN THE ABOVE A PREDETERMINED LEVEL, AND A SECOND STATE INDICATIVE OF THE ABSENCE OF FLAME IN SAID COMBUSTION CHAMBER WHEN THE ELECTRIC CHARGE STORED IN SAID SECOND STORAGE MEANS FALLS BELOW SAID PREDETERMINED LEVEL, AND MEANS TO TRANSFER ELECTRIC CHARGE FROM SAID FIRST STORAGE MEANS TO SAID SECOND STORAGE MEANS ONLY IN RESPONSE TO THE PRESENCE OF SAID FIRST DEMODULATOR OUTPUT SIGNAL TO CAUSE SAID CONTROL DEVICE TO ASSUME SAID FIRST STATE. 